1. Technical Field
This invention relates to a method of determining the degree of fatigue for metallic materials that constitute structures or machine components, such as pressure vessel.
2. Background Art
A conventional and popular method of determining the degree of fatigue for metallic materials is to measure the half-value width of an approximately selected X-ray diffraction spectrum, the change in which being related to the degree of fatigue. However, there are problems in this method, such as, for example, the changes in said half-value width and the changes in the degree of fatigue are not linerarly related as shown in FIG. 9; for another example, the half-value widths determined for cracked portion often differ greatly from those determined for parts away from the crack even for materials having expended their fatigue lifetimes, or of a degree of fatigue of 100%.
Although there are other methods available for estimating the degree of fatigue, such as by changes in the hardness and by those in the metallographic microstructure, none is accurate enough to be accepted generally.